The present invention relates to a system for raising and lowering the load support of an electric lift truck.
In an electric lift truck, the load is lifted by an electric motor which drives a pump which sends pressurized fluid through a hydraulic circuit to one or more hydraulic jacks which raise the support, for example forks, on which the load rests.
Normally, the electric motor which drives the pump is operated at two speeds only, namely a normal speed and a high speed, and the task of fine adjustment of the speed of rise of the forks is carried out by a hydraulic distributor which divides the flow of pressurized fluid sent to the hydraulic jacks. The operator moves a suitable control lever through which one of the two speeds of the motor is engaged and the distributor is operated: the position of the control lever corresponds to the required speed of rise.
The division of the flow of pressurized fluid results in the generation of heat and consequently the dissipation of energy. Evidently, a dissipation of energy results in a decrease in the duration of the charged state of the electrical accumulators of the truck and consequently a decrease in the operating range of the truck.
To lower the load, the control lever is moved in the opposite direction to the previous direction, and the distributor connects the fluid sent to the hydraulic jacks to a discharge system in such a way as to allow the forks to descend by gravity.
In lowering, therefore, there is a wastage of kinetic energy, which it would be very useful to recover.